This invention is directed to a method of delivering breathability and elasticity to a film in one step while making the film.
Breathable materials, such as breathable films, typically block the passage of particulate matter, water and other liquids while allowing water vapor and air to pass through the material. Thus, breathable materials are particularly suitable for use in garments and personal care products, thereby allowing moisture trapped beneath the fabric to escape as water vapor.
One example of a breathable material is a microporous film. This type of film is typically filled with particles or other matter and then crushed or stretched to form a fine pore network of micropores of a size and/or frequency to impart the desired level of breathability to the fabric.
Elasticity is another material attribute that is desirable in garments and personal care products. For example, in pant-like garments, machine direction elasticity is desirable because longitudinal conformability prevents a crotch region of the garment from sagging and bulging. Similarly, cross direction elasticity is desirable because lateral conformability maintains a snug, yet comfortable fit about a wearer""s hips. Furthermore, when elasticity is incorporated within the garment material, the need for adding elastic components to a product can be eliminated.
Materials that are both breathable and elastomeric can be formed by laminating a breathable layer with an elastomeric layer. However, breathable laminates are often not breathable enough, thereby resulting in excess vapor retention within the garment, personal care product, or other application made of the breathable laminate.
Another method of forming breathable, elastic materials is to include inorganic filler within an elastic/semi-rigid polymeric matrix, stretching to micro-void, thus gaining both breathability and elasticity. However, achieving a proper polymeric matrix blend is difficult, yet necessary, in order to obtain the desired balance of properties of breathability, extensibility, and retraction, along with other property improvements.
Yet another method of forming breathable, elastic materials includes aligning thin fibers of stretched elastic material along a spunbonded sheet, bonding the fibers to the sheet and then releasing the composite. However, this process can be time-consuming and expensive.
There is a need or desire for a cost-efficient, time-efficient method of producing elastic, breathable films.
The present invention is directed to a method of delivering breathability and elasticity to a film in one step during the extrusion/stretching process of making the film. The one-step method includes coextruding thin elastic fibers within the matrix of a filled, semi-rigid film structure and stretching the film structure to form micro-voids to gain breathability, while the elastic fibers within the film structure provide elasticity.
Various embodiments of the invention include the use of mono-axial stretching, along with bi-axial stretching. Also, the elastic fibers can be aligned in a machine direction pattern to create machine direction elasticity, and/or can be aligned in a cross direction pattern to create cross direction elasticity. Furthermore, absorptive characteristics can be added to the elastic fiber material to enhance the absorptive characteristics of the resulting film structure.
The resulting film structure can deliver breathability, expressed as water vapor transmission rate (WVTR), in a range of about 500 to 30,000 grams/m2-24 hours using the Mocon WVTR test procedure described below. The resulting film structure is particularly useful in diapers and other personal care products.
With the foregoing in mind, it is a feature and advantage of the invention to provide an efficient, low-cost method of delivering breathability and elasticity to a film during the film-making process.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the examples and drawings.